Struct egg::Extractor

pub struct Extractor<'a, CF: CostFunction<L>, L: Language, N: Analysis<L>> { /* fields omitted */ }

Extracting a single RecExpr from an EGraph.

use egg::*;

define_language! {
    enum SimpleLanguage {
        Num(i32),
        "+" = Add([Id; 2]),
        "*" = Mul([Id; 2]),
    }
}

let rules: &[Rewrite<SimpleLanguage, ()>] = &[
    rewrite!("commute-add"; "(+ ?a ?b)" => "(+ ?b ?a)"),
    rewrite!("commute-mul"; "(* ?a ?b)" => "(* ?b ?a)"),

    rewrite!("add-0"; "(+ ?a 0)" => "?a"),
    rewrite!("mul-0"; "(* ?a 0)" => "0"),
    rewrite!("mul-1"; "(* ?a 1)" => "?a"),
];

let start = "(+ 0 (* 1 10))".parse().unwrap();
let runner = Runner::default().with_expr(&start).run(rules);
let (egraph, root) = (runner.egraph, runner.roots[0]);

let mut extractor = Extractor::new(&egraph, AstSize);
let (best_cost, best) = extractor.find_best(root);
assert_eq!(best_cost, 1);
assert_eq!(best, "10".parse().unwrap());

Implementations

impl<'a, CF, L, N> Extractor<'a, CF, L, N> where
    CF: CostFunction<L>,
    L: Language,
    N: Analysis<L>, 

pub fn new(egraph: &'a EGraph<L, N>, cost_function: CF) -> Self

Create a new Extractor given an EGraph and a CostFunction.

The extraction does all the work on creation, so this function performs the greedy search for cheapest representative of each eclass.

pub fn find_best(&self, eclass: Id) -> (CF::Cost, RecExpr<L>)

Find the cheapest (lowest cost) represented RecExpr in the given eclass.

pub fn find_best_node(&self, eclass: Id) -> &L

Find the cheapest e-node in the given e-class.

pub fn find_best_cost(&self, eclass: Id) -> CF::Cost

Find the cost of the term that would be extracted from this e-class.

Trait Implementations

impl<'a, CF: Debug + CostFunction<L>, L: Debug + Language, N: Debug + Analysis<L>> Debug for Extractor<'a, CF, L, N> where
    CF::Cost: Debug, 

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.